NSF Research Experience for Undergraduates

GL and DTM have a joint summer intern program for college undergraduates.

Photo from January 2010 American Astronomical Society Meeting in Washington, DC. Pictured from left to right are: Rebecca Rattray (senior Vanderbilt University), Anna Hughes (graduate student, University of Colorado), Alycia Weinberger, Johanna Teske (graduate student, University of Arizona), Alicia Aarnio (graduate student, Vanderbilt University)

Projects

Rebecca Ratray, Vanderbilt University, 2009
- Advisors: Alycia Weinberger and Guillem Anglada
- Title: Calculating Distances and Motions of Stars in the TW Hydrae Association
- Abstract:Distances and proper motions were determined for seven stars of the TW Hydrae association (TWA) using images from the Carnegie Astrometric Planet Search Camera (CAPSCam) on the 100-inch telescope at Las Campanas Observatory. The stars of TWA appear to be transitioning from having the material necessary to form gas giant planets to the late stages of planet formation. In order to study the conditions surrounding these stars and to calculate their age, distances must first be determined. Spatial velocities were calculated from the distances and proper motions measured. The age of TWA was estimated by plotting the positions and velocities of the stars and calculating the instant of closest approach, but the age calculated (1.82 plus/minus .43 Myr) was inconsistent with previous estimates of the age of TWA (5 - 10 Myr), which may suggest that the association is not expanding as expected, or that it is larger than expected. The age of TWA was also estimated by plotting TWA stars on the Hertzprung-Russell diagram and comparing their luminosities to models of pre-main sequence evolution. The TWA stars all had model ages between 2 Myr and 20 Myr. The distance and motion of TWA 14 are inconsistent with those of the other known TWA members; we therefore propose that TWA 14 may not be a member of TWA.
Caroline Walker, Bethesda Chevy Chase High School, 2009
- Advisor: Alycia Weinberger
- Title: Parallactic Distances to Brown Dwarfs
Laura Flagg, University of Chicago, 2008-2009
- Advisor: Alycia Weinberger
- Title: Detectability of Comet Impacts on Exo-jovian Planets
- Abstract:
  The first imaged exosolar planets are around stars with circumstellar debris disks, and the dust in these disks arises from the collisions of planetesimals. We consider the detectability of planetesimal impacts on imaged exosolar planets by using Jupiter during the 1994 Comet Shoemaker-Levy 9 events as a proxy. By integrating the whole planet flux with and without impact spots, we measure the effect of the impacts at wavelengths from 2 - 4 micron. This wavelength range is suitable for imaging exosolar planets with ground-based adaptive optics systems. The impactors deposited material high-up Jupiter's atmosphere. Jupiter's reflected light spectrum in the near-infrared is dominated by methane opacity, and at wavelengths deep in the methane bands such as 2.3 and 3.5 micronm, where the planet would normally have low reflectivity, it brightened substantially and stayed brighter for at least a month. We quantify these effects and timescales and estimate the likelihood of impacts onto giant planets throughout Solar System-like dynamical histories.
Johanna Teske, American University, 2007-2008 (Senior Thesis)
- Advisor: Alycia Weinberger
- Title: Circumstellar Disk Astrochemistry
- Abstract: There are important stages of disk evolution that are not well understood; this Capstone focuses on debris disks, representing an intermediate stage between gas-rich protoplanetary disks and established planetary systems. To further understand the complex interaction of gas and dust in these disks, the optical spectra of A-shell stars were examined via measurement of absorption line strength and radial velocity to characterize their circumstellar material and diagnose why some stars show little evidence for a dust component, while others have significant infrared excess.
- Current Work: Gradute student at Universerity of Arizona, Astronomy Department
Daniel Poore, Wilson High School, 2006
- Advisor: Alycia Weinberger
- Title: Detectability of Comet Impacts on Exo-jovian Planets
- Abstract:
  Using data from the 1994 impact of Comet Shoemaker-Levy 9 onto Jupiter, we are studying the observability of such events on exosolar giant planets.
Alicia Aarnio, Smith College, 2004 and 2005
- Advisor: Alycia Weinberger
- Title: New Members of the HD 141569 Association
- Abstract:
  Following up on the discovery of two stars associated with HD 141569, searches of a region of sky surrounding the star turned up 43 potentially young stars with similar proper motions to HD 141569. Analyzing the spectroscopic data of these stars, their Li 6708A equivalent widths were taken and radial velocities were found. An approximate stellar age of between 5-10 Myr was determined; this age is in agreement with previous findings for HD 141569 and its companions. The space motions of these young stars were calculated and 6 stars were found to have U, V, and W values within one sigma of uncertainty. These space motions when combined with Li equivalent widths conclusively prove membership to the association.
  See our paper: Aarnio et al. 2008
- Current Work: Gradute student in Vanderbilt University Astronomy Department, PhD expected 2010
Matthew Peck, University of Maryland, Baltimore County, 2003
- Advisors: Aki Roberge and Alycia Weinberger
- Title: Compositional Analysis of Variable Gas in the Beta Pictoris Debris Disk
- Abstract:
  Beta Pictoris is surrounded by a debris disk which was discovered due to excess infrared emission. The orientation of Beta Pictoris makes it an ideal candidate for study. The disk is edge on, directly in the line of sight. Therefore, solar radiation must pass directly through the disk. For a long time, Beta Pictoris has been known to have time variable absorption lines. It is believed that these variable lines are caused by the presence of bodies, such as comets, evaporating upon falling into the star. I have been studying the time variable gas component of the disk and have found the presence of heavy elements with non-solar abundances. The elements identified are Fe, C, Si, Ni, S, Cr, Mn, and Al. With Space Telescope Imaging Spectrograph data using ultraviolet echelle spectroscopy, I have calculated the column densities of these elements at 4 distinct velocity ranges. From these column densities I calculate the excitation temperatures of the gas as well as the relative abundance of the elements.
Anna Haugsjaa, University of Montana, 2002
- Advisor: Alycia Weinberger
- Title: A Search for Vega-like Stars in the TW Hydra Association
- Abstract:
  Vega-like stars, which possess dusty circumstellar disks, can provide us with clues as to the origin of our solar system, also born of a circumstellar disk. By studying Vega-like stars of different ages and how they are distributed in space, age, and spectral type, we can begin to understand the conditions under which planets form and better constrain the events that can lead to planet formation.
  The TW Hydrae Association was targeted for this study because it is a young association, around 8 million years, and is already known to possess four Vega-like stars. It is also relatively nearby, which makes further, detailed study of the stars and their disks feasible for a later date.
  The data for this project was taken using the Keck long wavelength spectrometer. Data was collected at the L, N and Q bands (4, 12, and 18 microns respectively) and analyzed using photometry, which measures the amount of radiation output by the source. Once magnitudes at these wavelengths were determined, an estimate of the star's photospheric flux at the N and Q bands was made and compared with the measurement for any sign of excess attributable to a cooler disk of material.
  The completion of the analysis of this data led to the discovery of two new Vega-like star candidates. A limit was also put on the amount of dust which could potentially be around the other stars in the survey.
- Current Work: Gradute student in University of Colorado Astronomy Department, PhD expected 2010
Leah Hutchison, Massachusetts Institute of Technology, 2002
- Advisor: Steve Desch
- Title: Mineralogy of Silicate Dust Grains in the Circumstellar Disk around TW Hydra
- Abstract:
  We place constraints on the composition of the dust in the protoplanetary disk surrounding the T Tauri star TW Hydra by computing spectral energy distributions (SEDs) and comparing them to observed infrared fluxes. The emergent spectrum from the assumed passive disk is calculated using a "1.5-D" radiative transfer code. The vertical temperature distributions of several dust populations are solved from simultaneously in each annulus of the disk, and the emergent spectra from all annuli are summed to produce the SED. The moment equations are closed using the approach of variable Eddington factors, which we solve for using ray tracing. Our approach includes scattering.
  Our calculations largely confirm the results of Chiang & Goldreich (1997), who attribute 10 um silicate emission features seen in protoplanetary disks to a superheated dust layer. Our computed SEDs provide a good fits to the 8-12 um observations of Weinberger et al. (2002) provided the maximum radius of the dust grains in the superheated layer is 1.5 um, and the dust grains are mostly amorphous, Fe-rich silicates. We suspect the presence of crystalline silicates, but are unable to quantify upper limits to the amounts.